GADD153 is a highly conserved mammalian gene whose expression is increased in response to a variety of stresses including growth arrest and DNA damage. A member of the CCAAT/enhancer-binding protein (C/EBP) family of transcriptional activators, it can dimerize with other C/EBPs through a leucine zipper domain. However, in contrast to other C/EBPs, it lacks the ability to bind to CCAAT DNA sequences and has therefore been proposed to serve as a negative regulator of other members of this family (by virtue of its ability to heterodimerize with them and inhibit their binding to DNA). Members of the C/EBP family are thought to play important roles in adipocyte differentiation and liver specific gene expression. Studies in our laboratory suggest that C/EBPs are also likely to serve a more ubiquitous role in regulating gene expression during the cellular response to stress. Studies in this project have focused on (1) the regulation and function of GADD153 in response to diverse environmental stresses; (2) definition of critical regulatory elements in the GADD153 promoter which control its activity in response to stress, and (3) examination of interactions between GADD153 and other related transcription factors during various conditions of stress. The most important finding during the past year has been the demonstration that GADD153 interacts directly with C/EBP beta during the cellular response to treatment with arsenite, a metabolic stress. Based on these interactions, the kinetics of GADD153 and C/EBP beta induction following exposure to arsenite, and additional observations indicating that C/EBP beta can transactivate the GADD153 promoter through interaction at a C/EBP binding site, we have proposed a model whereby GADD153 acts through an autoregulatory feedback loop to attenuate its own expression through interference with C/EBP beta. In addition we have obtained preliminary evidence to suggest that other transcription factors including ATF3 and junD also contribute to regulate the transcriptional activity of the GADD153 promoter during stress. Current studies are aimed at further defining their role in regulating GADD153 expression.